A vehicle, such as a car, includes a speed control system comprised of a drive system and a braking system. The drive system includes an accelerator pedal linked, either mechanically or as part of a drive-by-wire system, to an engine. The position of the accelerator pedal configures the engine to output an engine torque, which engine torque is transferred along a drive train to a set of wheels for moving the car. The braking system includes a brake pedal which when depressed actuates the system by pressing brake pads against brake discs which are associated with two or more of the vehicle wheels, thereby slowing down the rotation of the discs on the wheels and braking the wheels to slow down the vehicle.
The vehicle pedals offer suitable locations for providing haptic feedback to a driver. For example, the feedback delivered to the driver through the accelerator pedal may include, but is not limited to, a warning about excessive speed, of approaching road conditions, or more generally to alert the driver if the vehicle is not being driven in a fuel efficient manner. Feedback delivered via the brake pedal may include, but is not limited to, warnings about loss of traction with the road surface or insufficient pressure on the pedal to avoid a perceived hazard ahead. The haptic feedback is typically delivered by a mechanism that produces a vibration in the pedal.
Whilst conventional vibration mechanisms, such as those generated by torque motors or magnetic actuators, may be used to generate haptic feedback, such mechanisms are relatively bulky and hence awkward to accommodate within the confines of a typical vehicle pedal. Accordingly, the use of piezoelectric elements offers a convenient means for generating haptic feedback to the driver, such elements being able to generate a pulse by rapid deformation and thereby simulate vibration. Moreover, being relatively compact and with a low profile, piezoelectric elements are simple to install without necessitating modification of existing pedal assemblies, and are easily replaceable.
Whilst existing haptic feedback systems employing piezoelectric elements provide several benefits, a problem exists in that some systems require more energy to be used than is desirable. This can prohibit use across a manufacturer's full vehicle range.
It is an object of the present invention to address disadvantages associated with such existing systems.